Summary/Abstract Project 3 consists of four specific aims all involved in understanding the role of paraoxonases 1 and 2 (PON1 and PON2) in modulating oxidative stress-induced neurotoxicity. Aim 1 will examine the role of PON1 status in modulating exposure to organophosphorus (OP) insecticides by utilizing a new biomarker, adducts to red blood cell acylpeptide hydrolase (RBC APH). It is expected that individuals with the capability for high rates of OP detoxication will exhibit lower levels of modification of the active site serine of RBC APH, as assessed by mass spectrometry. Aim 2 will examine the modifications of mouse paraoxonase 1 (MoPON1) resulting from exposures to manganese (Mn) and cadmium (Cd). A sub-aim of Aim 2 will explore the fate and function of recombinant mouse PON2 (rMoPON2) injected into PON2-/- mice which are less able to modulate oxidative stress. PON2 appears to protect PON1 from the effects of oxidative stress. This aim is based on a recent finding that under conditions of oxidative stress, the catalytic domain of PON2 is found on the outside of cells where it protects the membrane lipids from oxidation. Aim 3 will examine the modulation of PON2 levels by estrogens and dopamine in the CNS and the role of microglial PON2 in the neuroprotective effects of estrogens. The structure of a higher molecular weight splice variant of PON2 will also be determined. It also aims to develop a protocol for determining PON2 status by examining the levels of PON2 protein, activity and mRNA in mouse and human macrophages. PON2 levels in males, and in pre- and post-menopausal women will be analyzed. Aim 4 will examine the role of PON2 in modulating susceptibility to the neurotoxicants Mn and Cd, both of which are known to induce oxidative stress. Altogether, the proposed experiments will provide novel information on the role of PON1 and PON2 in modulating oxidative stress and protecting individuals from cardiovascular and neurological diseases.